A reporter is something that returns a value and, unlike a command, cannot be a stand-alone code element . NetLogo has some useful built-in reporters that cannot be changed directly such as ticks, pi, e, world-width, and world-height. For example, we cannot just write ticks in the code. We need to use ticks in some other algorithm such as: if ticks > 9 [ wake-up ] or let world-area (world-width * world-height).

Other primitives that we use for filtering agentsets or manipulating lists such as of, with, sort-on, and word are reporters, too.

Many turtle, patch, and link properties such as color or label can be thought of as both variables that we can change with the set command, as well as reporters that provide us with the values of these variables. Notice in the following example that the brackets [ ] that come before

if xcor < 0 [ 
If [pycor] of patch-here > 0 [ 
set label “Quadrant II” ] 
]

Finally, you can create custom reporters using the to-report keyword to begin a reporter procedure and the report command at the end of your procedure, right before the end keyword. Reporters can be useful to tidy up your code and keep you from repeating lines of code; if you use the same equation or long line of code multiple times, a to-report procedure can be used to replace it.

For example, if you write ask turtles with [ shape = “person” and color = green and size > 5 ] many times, you could instead add a reporter procedure like

to-report big-green-people 
report turtles with [ shape = “person” and color = green and size > 5 ]
end

and then replace each turtles with [ shape = “person” and color = green and size > 5 ] for big-green-people in your code, such as ask big-green-people [ do-things ]. Once you have calculated the value you would like to return from the procedure, add the primitive report in front of the value.

to-report is often used for calculations. For example, if you want to calculate the area of circles many times in your code, you can write

To-report circle-area [ r ]
Report ( pi * ( r  ^ 2 ) )
end

Now, whenever you would like to calculate the area of a circle, simply write circle-area [ radius ].